The Gelsenkirchen side found themselves subjected to stiff criticism after Saturday's 2-0 loss at the BayArena, where goals from Andre Schurrle and Stefan Kiessling sent Stevens' side home with nothing.
It was hardly the ideal preparation for a match where victory would ensure the Bundesliga side's progress to the next stage, but Stevens is unconcerned.
"We have written off the Leverkusen game and the only thing we are focusing on now is to get to the next round," he told reporters.
"We accept the criticism for our performance against Leverkusen but what is more important is the entire picture after 34 league matches."
Stevens' bullish attitude came despite a series of injury concerns that are likely to see him denied the services of Ibrahim Afellay (thigh), Christoph Metzelder (groin) and Atsuto Uchida (thigh).
"Afellay is unlikely to play," he added. "It would be too dangerous to play him. Metzelder and Uchida are still building up intensity in training and it would be a risk to play them at this point.
"We still have to decide about that."
Their Greek opponents, who are two points behind their hosts on six and still have their own hopes of qualifying, warmed up for the contest with a regulation 2-0 win over minnows Kerkyra.
Boss Leonardo Jardim rang the changes for that game in a bid to keep his first-choice players fresh, meaning the likes of Kostan Manolas, Giannis Maniatis and Kostas Mitroglu should return.
Jardim was confident about his side's ability to progress in the competition, boldly targeting back to back victories over Schalke and Arsenal.
"There are still more six points to win and we intend on doing just that," he said.
"Our goal is to make it to the next phase. I'm doing the best job I can at Olympiacos. We are a new team compared to last year and we are improving steadily."